series, the movie is good but it is very short and sometimes the story is not developed with much depth, so prefer series. The one I like the most is Breaking Bad, I can't imagine how it would be in a movie, but it would certainly cut a lot of important things
The reason I prefer TV shows though is mostly because of the longform storytelling. When a TV show is great or at least very good, all the hours and seasons you get to watch of the show easily trumps the two hours that you get with a good movie.